1. Field of the Invention
This invention relates to an elastic support device for a shadow mask of a color picture tube, and more particularly an elastic support device for a shadow mask of a color picture tube, which is able to minimize stress of elastic members resulting from thermal expansion of the shadow mask during operation of the color picture tube, thereby improving compensation for mislanding of an electron beam emitted to a screen.
2. Description of Related Art
Generally, a color picture tube has, as shown if FIG. 1 of the accompanying drawings, a bulbiform exterior configuration comprising a panel 1, and a funnel 2 formed with a neck portion 2a having a reduced cross-section. An electron gun 3 is mounted within the neck portion 2a of the color picture tube to emit an electron beam 4, and a shadow mask 6 formed with small through-holes each having a diameter of the order of 0.3 mm is disposed within the enlarged portion of the funnel 2 opposite the neck portion 2a in spaced-apart relationship to the inner surface of the panel 1 so that the electron beam 4 emitted from the electron gun 3 passes through respective through-holes of the shadow mask.
In addition, a screen 5 having luminous fluroescent materials for red, green and blue colors coated thereon in a given pattern is attached to the inner surface of the panel 1 in parallel, spaced-apart relationship to the shadow mask 6, whereby the electron beam passed through the shadow mask lands on the luminous fluorescent materials coated on the screen to cause luminescence of the fluroescent materials coated on the screen, thereby forming a picture image on the screen. At this time, the interior of the color picture tube is maintained in a high vacuum state (of approximately 10 Torr) in order to enable the electron beam 4 to be accelerated and effectively land on the screen 5 coated with the luminous fluorescent materials.
With the color picture tube thus constructed, about 20% of the electron beam 4 emitted from the electron gun 3 mounted within the neck portion 2a passes through the small through-holes of the shadow mask 6, while the remaining 80% of the beam collides against the shadow mask, resulting in thermal expansion of the shadow mask made of a thin sheet having thickness of appoximately 0.2 mm. Such thermal expansion of the shadow mask due to the collisin of the electrom beam causes variation of the relative positions between the through-holes of the shadow mask 6 and the fluorescent materials for red, green, and blue colors coated on the screen 5, thereby giving rise to a scanning error and thus lowering color purity of the color picture tube. In order to eliminate such a phenomenon, therefore, elastic members(referred to as "corner springs") are disposed at a frame supporting the shadow mask, so that correction of the position variation as set forth above may be accomplished.
A prior art elastic member performing the function as described above is of the type shown in FIG. 2. The elastic member 8 is attached at one end thereof to the frame 7 supporting the shadow mask 6 and coupled at another end thereof to a panel pin 10 provided on the inner surface of the horizontally extending peripherey portion of the panel 1, so that it exerts elastic force upon the frame and cooperates with the frame to elastically support the shadow mask which is secured to the panel by means of the frame and the elastic member.
In this prior art, when heat is transmitted to the shadow mask 6 during operation of the color picture tube, the frame 7 supporting the shadow mask deforms due to thermal expansion of the shadow mask to exert compressive force upon the elastic member 8 secured to the lower portion of the frame.
As a result, the elastic member undergoes stress caused by the compressive force and is shifted along with the shadow mask and the frame from the position as indicated by the solid line in FIG. 2 to the position indicated by the dotted lines. At this time, if the relative positions between the mask and the frame deviate from the given allowable limits necessary for the design of the color picture tube, color purity of the picture tube is greatly lowered. Therefore, it is desired to meet the requirements that the relative positions must be maintained within the given allowable limits.
This prior elastic member is however disadvantageous in that when the member is thick so as to meet the requirements as set forth above, good elastic supportability may be obtained, but a spring-back phenomenon takes place during the forming operation, thereby making it difficult to carry out the forming operation, and to the contrary, when the elastic member is thin, the forming operation may be easily carried out, but the desired elastic supportability is not obtained.